Layout guidelines:
1. Within the battery limits of a process unit several furnaces in the same or different services, together with their associated close coupled equipment, may be located in a single area and shall be separated within that area only as required for operational and maintenance access.
2. Fired heaters are a constant source of ignition and should be located in accordance with Table 1 with the following expectations:
1. They shall be located 7600mm (25’- 0’) away from their fuel gas knock-out pot.
2. When the hydrocarbon being handled is above its auto-ignition temperature process equipment may be located close to the furnace, as long as there is access for fire fighting and maintenance.
1. Areas for furnace tub pulling may extend over roads which are peripheral to the unit and which are not required for access to other plant areas.
2. Furnaces shall be provided with platforms for operations and for access as follows:
1. For maintenance of soot blowers.
2. For burner operation when inaccessible from grade.
3. For observation doors except that when the doors are located less than 3600mm (12’ – 0’) above grade access shall be by ladder only.
4. When temporary platforms for header boxes containing removable plug fitting are required, only the platform support shall be provided.
5. Reforming and desulphuring furnaces may be located a minimum distance from their associated process equipment consistent with operating and maintenance requirements.
Direct fire heater piping guidelines:
1. Safety Features:
A. Lines shall not obstruct explosion doors or tube access doors.
B. Manifolds for heater snuffing steam shall be located at grade not less than 15m (15 ft) form the heater and preferably between the heater and control room.
1. Flow distribution and Manifolding
Where the service I such that unequal flow though any pass of the heater would result in deposition of coke I the tube, or overheating of the tube walls, some positive means shall be provided on each pass to adjust for unequal flow.
1. Inlet Piping
1. Inlet piping preferably should be symmetrical and of the same length from he point where flow splits to the heater inlets. This refers to the number of bends, elbows, valves as well as the length of straight runs of pipe and their location.
This is extremely important where the feed is mixed phase consisting of part vapour and part liquid.
2. For mixed phase flow to multiple pass heaters, the inlet manifold to the heater coils hall be sized on the basis of entrainment velocities, well within the turbulent flow region. In order to maintain, as far as practicable, a uniform mixture of liquid and vapour, particular attention shall be given to the configuration of the piping to avoid impact or impingement separation of the vapour and liquid ahead of the inlet of each tube pass.
3. For “all liquid” flow to multiple pass heaters, the inlet manifold shall be designed on the basis of symmetrical piping and moderate pressure drops.
2. Outlet piping
1. On outlet piping, symmetry, with respect to the number of fittings and the length of pipe, is not normally as critical as on the inlet. However, non-symmetrical piping may contribute to uneven heating and possible coking up and overheating of tubes.
3. Burner Piping
1. Flow of fuel to individual burners shall be adjusted by valves located so that the valves can be operated while observing the flames through peepholes or burner opening. However, valves must not be positioned below the base of the heater.
2. The burner feeds for gas and steam shall be taken from the top of the heaters.
3. Piping shall be arranged so that there will be no pockets in fuel gas lines in which condensate could collect.